Seven million years of human history is about to come to a end, what caused this  asteroid Collision? Nuclear war? Maybe even alien invasion? No it is the will of the gods, the ones who created man.
All gods of every religion and feath have  gathered to decide the feath of humanity.

It's about to start big sis hild. A young teenage girl side nervously, she had shoulder length lilac hair, wearing a green jacket over a white shirt with black shorts. On her left leg was a black stocking with a garter belt, sneakers and a hairclip in the shape of a wing.
( Goll youngest of the thirteen valkyrie sisters)

Next to Goll was a beautiful woman with midnight blue hair that reached her waist, wearing a formal white dress with a wing shape hairpin with beautiful emerald green eyes.
( Brunhilde oldest of the thirteen valkyrie sisters)

Brunhilde remained slight and watched the gods in the Council, in the middle of the room in a Royal looking throne sat a old man in a toga with a long white beard and eyebrows.
(Zeus chairman of the Council of Valhalla and King of the Olympians)

Well everyone it is quite sometime since we all have gathered together, now let's get started shall we. Zeus said. Standing by Zeus was a young man in a black suit, with red eyes and red markings on his face with black hair.
( Hermes one of the twelve Olympians)
Hermes held two signs, one had a X and the other a O.
So regarding the survival of mankind for the next thousands years. Should we forgive them? Or simply put them to an end? Zeus asked them,
Now show me the will of the gods.

Let's just gave them doomsday already, Shiva the Indian God of creation and destruction, a God with four arms and purple skin voted. From what I seen humanity has no interest in repenting or changing their ways so,why not give them the old fire and brimstone and when we're done with them can we try and evolving some other animal this time! Shiva said with little care for humanity.
N-no way... how could he... Goll said with slight

True, it is as Shiva says... in the last thousand years the earth has become too ugly. Agreed Aphrodite the Greek goddess of love and beauty. The seas filled with oil and waste, countless species of animals have gone extinct, forests destroyed. So, to speak humanity is the dangerous living cancer on the earth. Isn't this true? Aphrodite asked soon more gods agreed with the goddess.

This is just as big sis hild said before the will of the gods is to end. Then mankind is... Goll thought with dread.
There is no way to object the will of the gods once they have made the decision humanity surely be erased.

Well I guess we have come to an agreement, then mankind's fate is deci- Zeus began to say.

Please wait a second! Brunhilde shouted. Every God turned their attention to the valkyrie and muttered on why she would be here. Pardon my intrusion various gods. There is one thing I have to say she announced.

Mind your manners Brunhilde! Shouted the ravens of Odin, the Supreme Nordic God. You bastard half-god! Huginn the white raven shouted. How dare you open your filthy mouth in the presence of greatness! Muninn the black raven shouted.

It is true mankind is vulgar and extremely violent. But, to destroy them just like that, well it just seems quite dull. Brunhilde stated intriguing the Gods. Whether the survival of mankind has any value or not... with the might and mercy of the gods, why don't we test them? Brunhilde said.

Test them? How? Do you wish to flood the Earth? Muninn asked. Or perhaps pledge them in a eternal ice age?

No. But I have a more effective way to test them. Brunhilde answer. Gods vs mankind in an all-out struggle, better now as the Ragnarok she announced.

Ra‐Regnarok? Goll asked in confusion.

A one-on-one showdown between Gods and mankind. Brunhilde explains. Thirteen combatants from each side, the  first side to achieve seven victories wins. Of course if mankind is to lose seven times their fate is sealed. In an unlikely event that mankind is Victorious they may live for another Thousand Years.

Such a law was never used before since the creation of mankind, the reason for that is because their is no way that mankind would be able to defeat the gods.

Ha! I don't know what you're blathering about, but it's seems you valkyries don't understand a thing. Huginn stated.

Mankind is no match for the gods. Muninn added.

Your proposal is pointless! The ravens shouted.

So,  the will of the gods is to destroy mankind and avoid direct confrontation with mortals, am I right? Brunhilde stated. We wanted to destroy mankind without fighting them. We don't want to be put in the same ring as them. Hmm... don't tell me... you're all completely terrified aren't you. Brunhilde say with a bit of an atrocious grin.

Huh? S-Sister... Goll said in shock.

If so, then I'm terribly sorry I was saying such unnecessary things, my bad. Brunhilde said in a fake apologetic way.
Go ahead don't listen to me. Let's just forget about the whole thing.

P-Pleaes stop! What are you saying!? Forgot about Mankind you will be erased for saying that! Please just apologize for real! Big sis! Big sis! Goll begged.

But the gods let out a wave of faint Chuckles, like a parent going on along with their child's lame Game. But Brunhilde was still confident because making light of the pride and dignity of the gods, as the remark did enraged them. The gods started shouting curse at Brunhilde for the fact that if anyone suspects the gods being afraid of mankind would be the greatest humiliation of all time.

AHHHH, of course the gods would be angry! Big sis hild,  what in the world are you thinking! Goll said in fear. But Brunhilde still remained confident.

I knew it! Compared to humans the gods  are far more easier to taunt! Brunhilde though with a smirk.

Hohohoh...I see Ragnarok quite the interesting proposal. Zeus said calmly,getting up from his throne. Well said. Your proposal is an absolute... GOOD IDEA! Zeus shouted with complete joy. Besides, don't you think it's  been a long time since we have seen the MIGHT OF THE GODS! Zeus shouted with a look of complete insanity, unnerving Brunhilde. Shall we a showdown between the gods and mankind? Zeus slammed his gavel.

The Ragnarok, mankind's last chance of survival has begun.

Currently, Goll and Brunhilde were thinking over what just happened. Brunhilde had a calm expression on her face, while Goll looked like she was dead inside, she then soon fell to her knees.

What's wrong Goll. Brunhilde asked.

I can't stand it anymore. Big sis... Goll whined. Why did you object the will of the Gods and them angry! You're just asking to be killed! She shouted at Brunhilde.

Goll... you're an apprentice valkyrie, so you may not understand this yet...but the bond between mankind and us valkyries is...deeper than of the gods. Brunhilde said softly. There is no way I can...just abandon them.

Big sis... Goll said in awe of her sister putting her life on the line for the survival of mankind. B-But, can mankind really win? Do you think mankind really has a chance against the Gods? She asked.

No..." Brunhilde said bluntly. At least not on their own.

Th-Then how are we going to win!? Goll asked in panic.

There is a way to help them, I just have to gather the best that mankind has to offer. Brunhilde said with determination.

But suddenly a gray porter appeared in front of the valkyrie and out of came a young looking man, the man had short brown hair and was wearing a black suit with a magenta shirt and camera.

(Tsukasa Kadoya Kamen Rider decade)

I may have a solution to your problem. Tsukasa said as he approached the Valkyries. Brunhilde and Goll had looks of complete shock of what they just Witness.

And who are you supposed to be? Brunhilde demanded.

I'm just a passing through kamen rider, and I'm here to help you. Tsukasa answer the valkyrie. And there is no need to be so aggressive.

Why would you want to do that. Goll asked nervously as Tsukasa was walking closer to the duo. Simply, it's what I do as a kamen rider and humanity on several occasions proven to not be so bad. Tsukasa said.

Oh? And how do you intend do that? And what the hell are kamen riders? Brunhilde asked as she raised an eyebrow at the dimension traveler.

Tsukasa smirked at Brunhilde. It's simply I have the ability to travel to alternate worlds and dimensions, so I can gather the fighters you need, and kamen riders are heroes who fought for and saved Humanity and defeated monsters who could destroy the world.  Tsukasa answer and explained. Shocking Goll and gaining the interest of Brunhilde. I see, such a power would prove very useful. Brunhilde mused Goll looked at her with shock.

Sister, please don't accept his offer, this guy is giving me a bad feeling! He's dangerous, sister please! Goll begged.

Be quiet Goll. Brunhilde said sternly as Goll quickly silences herself as Brunhilde turned her attention back on Tsukasa. So you can truly me grant me access to these kamen riders and are they capable of going against the Gods? She question the kamen rider.

I can promise you that each and possible rider will be at your service. Tsukasa said with smirk.

Brunhilde smirk. Excellent then let's begin. She ordered as Tsukasa created another gray portal as Brunhilde and Tsukasa enter it, followed by Goll who could only look at Tsukasa nervously.

I got bad feeling about this. Goll thought as she entered the portal.

So is my prolong, I'll try being shorter  in the future  and I'm still not sure of who should fight in round one, I'm crossed between kiva and den-o, I'll let you guys vote in the comments. And I'll be posting my stuff about my undertale Au